Semiconductor materials are extensively used in many electronic applications. Semiconductors may be used as substrate materials which are processed using conventional techniques to form, for example, a variety of different semiconductor devices.
Ion implantation is a conventional process for introducing dopants into semiconductor materials. Oftentimes, semiconductor devices include doped regions which have an increased conductivity relative to the substrate material. Typically, during ion implantation, a desired dopant material is ionized in an ion source to form positive ionic species and electrons. The positive ionic species are accelerated at a selected energy to form an ion beam. The beam is directed at the surface of the wafer and the impinging ions penetrate into the bulk semiconductor material to form a region of the desired conductivity.
It generally is desirable to utilize an ion beam having a neutral space charge, wherein the charge from positive ionic species is balanced with the charge from electrons. Beams that have do not have a neutral space charge (i.e., beams that have either a positive or a negative space charge) may be difficult to transport and also may cause charge to build up on the wafer surface which can damage devices in the wafer. In some cases, ion sources generate beams that have a net positive charge. In particular, ion beams having a high beam current and/or a large area may have a net positive charge.
When beams having a net positive charge are generated, beam neutralization techniques may be employed. One conventional neutralization technique involves introducing electrons into the beam to compensate for the net positive charge. The electrons may be introduced downstream of the ion source, for example, using a plasma flood gun system. The net flux and energy of electrons emerging from the plasma flood gun, and the ion beam potential and charge distribution in the beam are important in determining the efficiency of the charge neutralization.
Implantation processes, and specifically the effect of charge neutralization techniques, have been characterized by measuring damage on devices resulting from an implant. Such characterization techniques involve exposing a test wafer to an implant step, followed by measuring the breakdown voltage and/or leakage current of devices on the wafer. In such techniques, the wafers must be removed from the process chamber of the implantation system to make the measurements, and the data is obtained after the implantation process. Thus, adjusting the system in response to the data may be difficult and time consuming.
Accordingly, there is a need for improved techniques that characterize semiconductor processes such as ion implantation and, particularly, techniques that measure the efficiency of charge neutralization methods.